/Engine/Source/Runtime/MaterialShaderQualitySettings/Classes/MaterialShaderQualitySettings.h
OverrideGetShaderPlatformQualitySettings()return value with the specified platform's settings. An empty PlatformName or otherwise non existent platform will causeGetShaderPlatformQualitySettings()to revert to its default behaviour.
void SetPreviewPlatform ( [FName](API\Runtime\Core\UObject\FName) PlatformName )